A number of problems in the petroleum industry derive from the viscosity, surface tension, hydrophobicity and density of crude oil. Heavy crude oil in particular, having an API gravity of less than 20 degrees, is difficult to transport due to its viscosity, and is difficult to remove from surfaces to which it has adsorbed, due to its hydrophobicity and immiscibility with water. Extra-heavy crude oil or bitumen, having an API gravity of less than 10 degrees, is heavier than water, so that it can sink to the bottom of a water formation, causing subsurface contamination.
The properties of crude oil contribute to the limitations of oil recovery from traditional oil fields. Conservative estimates suggest that 30% of the technically recoverable oil in U.S. oil fields is inaccessible due to the adsorption of the residual oil to porous geologies. Technologies to unlock the oil in these so-called “dead” wells presently involve the use of hot water injections with expensive surfactants, chemistries that are applied to overcome the hydrophobicity of the adsorbed oil so that it can be mobilized.
The properties of crude oil also contribute to the difficulty of environmental remediation following, for example, an oil spill onto a body of water. The high interfacial tension causes the oil to float on the water and adhere to plants, animals and soil. As the aromatic constituents of the oil evaporate, the heavier residues can sink, contaminating the subsurface structures. Current treatment of spilled oil on water surfaces relies on time-consuming and expensive biological degradation of the oil. Thick, adherent crude oil cause environmental problems in the oil fields as well. Oil deposits attached to vehicles and equipment must be cleansed with jets of hot water and caustics.
The viscosity of heavy crude oil makes the substance difficult and expensive to transport to upgrading facilities. Because of its viscosity, a significant amount of energy is required to pump it through pipelines to a refinery. Furthermore, the viscosity affects the speed at which the heavy crude oil can be pumped, decreasing the overall productivity of an oil field. Exploiting certain oil fields or other oil deposits may be economically unfeasible to develop at present because of the transportation-related costs.
Surfactants have been widely used in the petroleum industry to ameliorate the effects of crude oil's physical properties. Surfactant molecules consist of hydrophobic and hydrophilic parts. Their amphiphilic nature allows them to be adsorbed at an oil/water interface, forming micelles that allow the interfacial tension between oil and water to be reduced.
Surfactants are sometimes used for desalting of crude oil. Desalting refers to the process of removing salts from oil, making the oil more suitable for further refining. The salts are typically dissolved in water that is associated with oil, so the removal of water has multiple benefits. The presence of water reduces the energy content of oil, and it carries salts that can harm catalyst performance or cause corrosion. Ethoxylated nonylphenols have been used for desalting of crude oil, but these compounds pose hazards to the environment.
Furthermore, surfactant technologies for the aforesaid petroleum applications typically are expensive or must be used at high concentrations. Additionally, demulsification can prove to be difficult, as these surfactants are designed for emulsifying purposes. Demulsification typically requires added materials and steps to break up the emulsion, which increases the effective cost of use. Furthermore, the salts present in nature can inactivate many surfactant technologies. In addition, other surfactant technologies for petroleum applications are tailored only to oils of a limited composition.
The development of a technology that can provide emulsion and favorable transport properties while maintaining the ability to demulsify on demand, all under variable conditions of salinity, remains unmet in the art. Such a technology would have wide reaching impact across the oilfield chemical sector in applications such as those mentioned above, particularly if the material could be inexpensively produced and could be applied to a variety of oil types.